The present disclosure relates to semiconductor devices, lead frame assemblies, methods for fabricating semiconductor devices, and methods for fabricating lead frame assemblies. More particularly, the present disclosure relates to assemblies of surface mount lead frames, resin encapsulated semiconductor devices employing the lead frame assemblies, methods for fabricating the lead frame assemblies, and methods for fabricating the semiconductor devices.
In recent years, demands for smaller-size and higher-performance electronic apparatuses have lead to increased miniaturization of semiconductor devices. There are commercialized small-size resin encapsulated semiconductor devices employing lead frames, such as a land grid array (LGA) package, a quad flat non-leaded (QFN) package, a small outline non-leaded (SON) package, etc., in which elements are encapsulated on substantially only one side. These semiconductor devices are typically formed as follows. A sheet of metal base is initially processed by stamping, etching, etc. to form a multiple lead frame arrangement in which a plurality of lead frames are attached to rails. On the multiple lead frame arrangement, semiconductor elements are mounted, a resin is molded, etc. to form packages. The packaged lead frames are removed from the rails to obtain individual completed semiconductor devices.
In the multiple lead frame arrangement, typically, the lead frames are attached to the rails by tie bars, and the lead frames are removed from the rails by cutting the tie bars. However, when the tie bar is cut, large shear stress needs to be applied to the tie bar, and therefore, the package is likely to be damaged in the vicinity of the tie bar. It is contemplated that the tie bar may be narrowed to facilitate cutting. In this case, however, the tie bar may have insufficient holding strength. Therefore, an attempt has been made to provide an auxiliary tie bar around the tie bar (see, for example, Japanese Patent Publication No. H03-105959). The auxiliary tie bar is not attached to the lead frame, and a tip portion of the auxiliary tie bar is buried in the package resin. Because the lead frame is held by the tie bar and the auxiliary tie bar, the holding strength is increased. Moreover, the lead frame can be removed by pulling the auxiliary tie bar out of the package resin, and therefore, the package is less likely to be damaged compared to when a thicker tie bar is used.